The disclosure of the following priority application is herein incorporated by reference in its entirety: Japanese Patent Application No. 2000-379674 filed Dec. 14, 2000.
1. Field of Invention
The invention relates to a fabrication method for a projection optical system and an exposure apparatus, or an adjustment method for a projection optical system and an exposure apparatus. In particular, the invention relates to correcting (adjusting) residual aberration in a projection optical system provided in an exposure apparatus for projection exposing a mask pattern onto a photosensitive substrate.
2. Description of Related Art
When fabricating a microdevice (e.g., semiconductor devices, liquid crystal display, thin film magnetic head, and the like) in a photolithography process, an exposure apparatus for projection exposing a mask (or reticle and the like) pattern onto a photosensitive substrate (workpiece) is used. In this type of exposure apparatus, because a mask pattern image is faithfully projected onto a photosensitive substrate with high resolution, projection optical systems are designed having excellent optical properties sufficient to restrict various aberrations.
However, the optical properties of projection optical systems used in manufactured exposure apparatus differ from their intended design, and various aberrations remain due to a variety of causes. As disclosed in, for example, U.S. Pat. No. 6,268,903, technology for correcting residual aberration uses a correcting optical member having a surface that is worked (shaped) in a predetermined form.
The invention addresses the above issues. It is one object of the invention to provide a fabrication method for a correcting member, a projection optical system and an exposure apparatus, that is capable of easily determining a corrected surface form to be provided to the correcting member for correcting residual aberration (unnecessary residual optical characteristics), as the desired continuous surface. It is another object of the invention to provide a fabrication method for a correcting member, a projection optical system, and an exposure apparatus, that excellently corrects predetermined aberrations (unnecessary residual optical characteristics) remaining, and that is capable of excellently controlling the side-effects of wavefront aberrations, and the like, which are generated secondarily associated with aberration correction (correction of optical characteristics). It is a further object of the invention to provide a microdevice fabrication method capable of fabricating highly precise microdevices using an exposure apparatus having a projection optical system having superior optical characteristics with excellently corrected residual aberrations (unnecessary residual optical characteristics).
In order to address the above and/or other problems, a first aspect of the invention provides a fabrication method for a correcting member for correcting residual aberration in a projection optical system which projects a first surface image onto a second surface, the fabrication method for the correcting member including: a measurement step of measuring aberration remaining in the projection optical system; a hypothesis step of hypothesizing, based on predetermined functions, a corrected surface form to be provided to the correcting member; a calculation step of calculating wavefront (transmission wavefront, and the like) information of a light beam which passes through each of a plurality of regions on the correcting member having the corrected surface form hypothesized in the hypothesis step; and an evaluation step of evaluating the remaining aberration in the projection optical system when the hypothesized corrected surface form hypothesized in the hypothesis step is provided to the correcting member based on the measurement result in the measurement step and on the wavefront (transmission wavefront, and the like) information calculated in the calculation step.
A second aspect of the invention provides a fabrication method for a projection optical system for projecting a first surface image onto a second surface, the fabrication method including: a measurement step of measuring residual aberration remaining in the projection optical system; a hypothesis step of hypothesizing a corrected surface form to be provided to a correcting member in order to correct the residual aberration in the projection optical system; a calculation step of calculating wavefront (transmission wavefront, and the like) information of a light beam which passes through each of a plurality of regions on the correcting member having the corrected surface form hypothesized in the hypothesis step; and an evaluation step of evaluating the aberration remaining in the projection optical system to be provided with the correcting member based on the measurement result in the measurement step and on the wavefront (transmission wavefront, and the like) information calculated in the calculation step.
According to a preferred embodiment for practicing the first and second aspects of the invention, the measurement step includes a first measurement step of measuring predetermined aberration remaining in the projection optical system, and a second measurement step of measuring wavefront aberration remaining in the projection optical system. Alternatively, it is preferred that the measurement step include a wavefront aberration measurement step of measuring wavefront aberration remaining in the projection optical system, and an extraction step of extracting predetermined aberration components by analyzing wavefront aberration measured in the wavefront aberration measurement step.
According to the preferred embodiment for practicing the first and second aspects of the invention, the measurement step measures each aberration at a plurality of measurement points in the projection visual field of the projection optical system. Also, it is preferred that the measurement step includes a step of measuring distortion aberration as the aberration. Additionally, it is preferred that the measurement step measures aberration remaining in the projection optical system with the correcting member set in the optical path before working, or that the measurement step measures aberration remaining in the projection optical system with the measuring member, having the same light characteristics as the correcting member before working, set in the optical path.
According to the preferred embodiment for practicing the first and second aspects of the invention, the evaluation step includes a first evaluation step of evaluating the predetermined aberration remaining in the projection optical system when the corrected surface form hypothesized in the hypothesis step is provided to the correcting member based on the measurement results of the predetermined aberration measured in the measurement step and on the wavefront (transmission wavefront, and the like) information calculated in the calculation step, and a second evaluation step of evaluating the wavefront aberration, not including the predetermined aberration component, remaining in the projection optical system when the corrected surface form hypothesized in the hypothesis step is provided to the correcting member based on the measurement results of wavefront (transmission wavefront, and the like) aberration measured in the measurement step and on the wavefront information calculated in the calculation step.
According to the preferred embodiment for practicing the first and second aspects of the invention, the calculation step includes an approximation step of approximating the corrected surface form with a Zernike function for each region of the correcting member having a corrected surface form hypothesized in the hypothesis step, and calculates changes in the wavefront of the light beam wavefront (transmission wavefront, and the like) which passes through each region based on the Zernike function approximated in the approximation step. Also, it is preferred that each region of the correcting member be the center of each evaluation point that the principle ray, shot into each measurement point in the projection optical field of the projection optical system, passes through the correcting member, and is defined as a region through which a light beam reaching the second surface, including the principle ray, will pass.
According to the preferred embodiment for practicing the first and second aspects of the invention, the hypothesis step hypothesizes a corrected surface form to be provided to the correcting member based on a Fourier function, a Zernike function and an exponential function. Also, it is preferred that the hypothesis step initially hypothesize a corrected surface form as a predetermined curved surface to be provided to the correcting member based on the measurement results in the measurement step, or that the hypothesis step initially hypothesize a corrected surface form as a plane to be provided to the correcting member.
According to the preferred embodiment for practicing the first and second aspects of the invention, the correcting member is an optical member with a plane-parallel form placed in the optical path between a lens component positioned on the first surface of the projection optical system and the first surface, or placed in the optical path between a lens component positioned on the second surface of the projection optical system and the second surface. Alternatively, it is preferred that the correcting member be a lens component placed on the first surface or the second surface of the projection optical system.
According to the preferred embodiment for practicing the first and second aspects of the invention, a corrected surface form decision process which obtains a final corrected surface form by modifying the parameters of the predetermined functions and repeating the hypothesis step, the calculation step and the evaluation step is included in order to improve residual aberrations in the projection optical system. In such a case, it is preferable that a working step be included for working (machining, polishing, and the like) the surface of the correcting member in order to provide to the correcting member a final corrected surface form obtained in the corrected surface form decision process. Alternatively, it is preferable that a working step be included to work (machining, polishing, and the like) the surface of the correcting member in order to provide to the correcting member a final corrected surface form obtained in the corrected surface form decision process, and a placement step of placing the correcting member, which has been worked in the working step, between the first surface and the second surface.
A third aspect of the invention provides a fabrication method for an exposure apparatus which includes a first placement step of placing a mask stage, to dispose a mask on the first surface, on a main body of an exposure apparatus; a second placement step of placing a substrate stage, to dispose a photosensitive substrate on the second surface, on the main body of an exposure apparatus; a third placement step of placing a projection optical system, fabricated according to the fabrication method in the second aspect of the invention, on the main body of an exposure apparatus; and a fourth placement step of placing an illumination system, for illuminating the mask placed on the first surface, on the main body of an exposure apparatus.
A fourth aspect of the invention provides a fabrication method for a microdevice which includes an exposure step of exposing the mask pattern onto a photosensitive substrate using an exposure apparatus fabricated according to the fabrication method in the third aspect of the invention, and a development step of developing the photosensitive substrate exposed in the exposure step.
A fifth aspect of the invention provides an adjustment method of an exposure apparatus having a projection optical system for projecting a mask pattern onto a photosensitive substrate, the adjustment method including: a measurement step of measuring remaining aberration in the projection optical system; a hypothesis step of hypothesizing, based on predetermined functions, a corrected surface form to be provided to a correcting member; a calculation step of calculating wavefront (transmission wavefront, and the like) information of a light beam which passes through each of a plurality of regions on the correcting member having the corrected surface form hypothesized in the hypothesis step; and an evaluation step of evaluating the remaining aberration in the projection optical system when the hypothesized corrected surface form hypothesized in the hypothesis step is provided to the correcting member based on the measurement result in the measurement step and on the wavefront information calculated in the calculation step.
According to a preferred embodiment for practicing the fifth aspect of the invention, the measurement step includes a first measurement step of measuring a predetermined aberration remaining in the projection optical system, and a second measurement step of measuring a wavefront aberration remaining in the projection optical system. Alternatively, the measurement step includes a wavefront form measurement step of measuring a wavefront aberration remaining in the projection optical system, and an extraction step of extracting predetermined aberration components by analyzing the wavefront aberrations measured in the wavefront aberration measurement step. Also, it is preferable that the measurement step measure each aberration in a plurality of measurement points in the projection optical field of the projection optical system. Additionally, it is preferable that the measurement step include a step of measuring distortion aberrations as aberrations.
According to the preferred embodiment for practicing the fifth aspect of the invention, the evaluation step includes a first evaluation step of evaluating the predetermined aberration remaining in the projection optical system when the corrected surface form hypothesized in the hypothesis step is provided to the correcting member based on the measurement results of the predetermined aberration measured in the measurement step, and on the wavefront information calculated in the calculation step, and a second evaluation step of evaluating the wavefront aberration, not including the predetermined aberration component, remaining in the projection optical system when the corrected surface form hypothesized in the hypothesis step is provided to the correcting member based on the measurement results of wavefront aberration measured in the measurement step and on the wavefront (transmission wavefront, and the like) information calculated in the calculation step.
According to the preferred embodiment for practicing the fifth aspect of the invention, the calculation step includes an approximation step of approximating the corrected surface form with a Zernike function for each region of the correcting member having a corrected surface form hypothesized in the hypothesis step, and calculates changes in the wavefront of the light beam wavefront (transmission wavefront, and the like) which passes through each region based on the Zernike function approximated in the approximation step. Also, it is preferable that each region of the correcting member is the center of each evaluation point which the principle ray, shot into each measurement point in the projection optical field of the projection optical system, passes through the correcting member defined as a region through which a light beam reaching the second surface, including the principle ray, will pass.
According to the preferred embodiment for practicing the fifth aspect of the invention, the hypothesis step hypothesizes a corrected surface form to be provided to the correcting member based on a Fourier function, a Zernike function and an exponential function. It is preferable that the hypothesis step initially hypothesize a corrected surface form as a predetermined curved surface to be provided to the correcting member based on the measurement results in the measurement step, or the hypothesis step initially hypothesize a corrected surface form as a plane to be provided to the correcting member.
According to the preferred embodiment for practicing the fifth aspect of the invention, the adjustment method includes a corrected surface form decision process which obtains a final corrected surface form by modifying the parameters of the predetermined functions and repeating the hypothesis step, the calculation step and the evaluation step in order to improve residual aberrations in the projection optical system. In such a case, it is preferable that the adjustment method include a working step to work (polishing, and the like) the surface of the correcting member in order to provide to the correcting member a final corrected surface form obtained in the corrected surface form decision process, and a placement step of placing the correcting member, which has been worked (polishing, and the like) in the working step, between the first surface and the second surface. The fifth aspect of the invention described above is an adjustment method for an exposure device, but may also be an adjustment method for a projection optical system.
A sixth aspect of the invention provides a fabrication method for a microdevice which includes an exposure step for exposing the mask pattern onto a photosensitive substrate using an exposure apparatus adjusted according to the adjustment method in the fifth aspect of the invention, and a development step for developing the photosensitive substrate exposed in the exposure step.